1. Field of the Invention
The present invention relates to power amplifiers, and more particularly, to a power amplifier with a variable supply of bias power according to a look-up table having a voltage value determined based on a level of an RF signal being input to the power amplifier to thereby increase power efficiency.
2. Description of the Related Art
Mobile communications terminals have been widely used because they are easy to use. As the use of these mobile communications terminals has increased, it has become important to run various kinds of applications to meet consumer demand and allow for long-time use at the same time.
In order to extend the use time of a mobile communications terminal, it is important to increase battery capacity. However, the size of batteries is limited since small, lightweight, and thin mobile communications terminals are in demand in the market. Therefore, there is a need to increase the power efficiency of main elements inside a mobile communications terminal. In order to transmit and receive RF signals, this mobile communications terminal uses a power amplifier. This power amplifier takes up a considerable portion of the overall power consumption of the mobile communication terminal. Thus, there is a need to increase the power efficiency of the power amplifier.
Meanwhile, this power amplifier is generally manufactured using a compound semiconductor. However, with the increase of manufacturing costs and advancements in a complementary metal oxide semiconductor (CMOS) process and circuit design, the number of power amplifiers being manufactured by the CMOS process has been gradually increased.
Though these power amplifiers need to satisfy linearity being demanded by consumers, since there is a trade-off between linearity and power consumption, power amplifiers are designed to satisfy linearity at the maximum power output level.
However, general power amplifiers output signals below the maximum power output level, and power consumption and linearity at the time need to be satisfied.
In the related art, the bias of an amplification unit is controlled by receiving an output signal as a feedback signal. In this case, however, it is difficult to implement a detection circuit due to a high power output level. As for the CMOS process, a CMOS device can be destroyed due to a low break down voltage. If bias control is continuously made, envelope information may be damaged.
Furthermore, the use of parallel amplification units operating at different signal levels causes an increase in circuit size and hinders input and output matching.